The present invention relates to an elastomeric thermoplastic polyolefin composition having a good softness and workability.
The composition of the present invention can be used in any process wherein elastomeric thermoplastic polyolefin compositions are needed. In particular, the composition of the present invention is suitable for being used in injection and co-injection moulding, blow-moulding and extrusion processes.
A number of physical and mechanic properties of the composition of the present invention, in particular the opaque appearance and softness, makes such composition particularly suitable for the production of manufactured articles having a good soft-touch feeling. Typical articles produced with the composition of the present invention are synthetic leathers (such as extruded films and sheets or extruded profiles) and shaped articles (such as soles for shoes). The main uses of articles having said features are in the vehicle field, in particular, to produce internal parts of vehicles.
Polymers and copolymers suitable for production of manufactured articles by injection, co-injection moulding and sequential injection moulding processes are already known. Such compositions are described in U.S. Pat. No. 5,480,942 (Spherilene) and patent application WO 96/22327 (Commer), for instance. Both the documents describe olefin polymers grafted with polyalkenylenes, in particular polyoctenylenes. The process for the preparation of said grafted polymers comprises the use of radical initiators.
Manufactured articles prepared from the polymers of above-mentioned prior art are transparent and have a bright appearance (namely, high gloss values). Contrary to this, at present it is requested that manufactured articles used to coat internal parts of vehicles be opaque.
Moreover, although the cited compositions are soft, they do not meet the present requirements entirely, as to meet them it is necessary to produce soft compositions.
Finally, the above-mentioned prior art compositions have the drawback of showing a marked stickiness, badly affecting the aesthetic appearance.
To overcome the drawbacks of the known polymers and meet the said requirements, now a new composition has been found which has higher softness and less stickiness.
Besides, the manufactured articles produced with the composition of the present invention are opaque.
Another advantage given by the composition of the present invention concerns the good workability of the composition in a broad range of temperatures. One does not observe a meaningful variation of the proprieties of the compositions in such range, with particular reference to the surface reproducibility, i.e. a good and constant quality of the embossing or roughness, planarity of the moulded surface and absence of the stickiness even after ageing.
A further advantage of the composition of the present invention is that it has good softness even in the absence of the extender oil. As well known the extender oil can be released by the composition containing it as time passes and cause pollution and fogging. Moreover, articles obtained by the composition containing extender oils can become gloss and greasy because of the emergence of said oil.
Therefore, an object of the present invention is an elastomeric thermoplastic polyolefin composition comprising (percent by weight):
(I) 40-97%, preferably 45-95%, of a heterophasic olefin polymer composition comprising:
(A) 5-50%, preferably 10-40%, of a crystalline propylene homopolymer with isotactic index greater than 80%, preferably from 85 to 90%, or crystalline copolymer of propylene and ethylene or a CH2xe2x95x90CHR xcex1-olefin, wherein R is a C2-C8 alkyl radical, or crystalline copolymer of propylene, ethylene and a CH2xe2x95x90CHR xcex1-olefin, wherein R is a C2-C8 alkyl radical, or blend thereof; said copolymers containing more than 85% of propylene and having an isotactic index greater than 80%;
(B) 0-20%, preferably 0-15%, of a crystalline copolymer fraction of ethylene with propylene or with a CH2xe2x95x90CHR xcex1-olefin, wherein R is a C2-C8 alkyl radical, or both propylene and said alpha-olefin, said fraction being insoluble in xylene at ambient temperature, i.e. 25xc2x0 C.; and
(C) 40-95%, preferably 50-75%, of an elastomeric copolymer fraction of ethylene with propylene or with a CH2xe2x95x90CHR xcex1-olefin, wherein R is a C2-C8 alkyl radical, or both propylene and said alpha-olefin, and optionally with minor amounts of a diene, said copolymer fraction containing ethylene in an amount smaller than 40%, preferably from 20 to 38%, and being soluble in xylene at ambient temperature;
(II) 3-60%, preferably 5-55%, of an elastomeric polymer having a hardness (Shore A, ASTM D-2240) equal to or less than 90 points, preferably equal to or less than 88 points, more preferably equal to or less than 75 points, selected from the group consisting of:
1copolymers of ethylene with a C3-C10xcex1-olefin containing at least 20 wt %, preferably from 20 to 70 wt %, of C3-C10 xcex1-olefin (13C-NMR analysis) and having a Mw/Mn ratio less than 4, preferably less than 3;
2 ethylene-methyl acrylate copolymers containing from 15 to 30 wt % of methyl acrylate units and having MFR from 1 to 10 g/10 min (ASTM D-1238);
3 saturated or unsaturated styrene block copolymers, linear or branched, containing at least one comonomer selected from butadiene, butylene, ethylene and isoprene; and
4 unsaturated norbornene polymers having a molecular weight over 3,000,000.
Examples of heterophasic olefin polymer composition (I) are described in published European patent application EP-A-0472946 (Himont Inc.), the content of which is incorporated herein by reference.
As a way of example the total amount of ethylene in heterophasic olefin polymer composition (I) is 15 to 35% by weight. Besides, the intrinsic viscosity of fraction (C) generally is 1.5 to 4 dl/g.
Preferably the propylene content in copolymers of fraction (A) is 90 to 99% by weight. The isotactic index is determined as the insoluble fraction in xylene at 25xc2x0 C. (see note 1 below).
Preferably the amount of ethylene in fraction (B) is at least 75% by weight, more preferably at least 80% by weight, with respect to the total weight of (B). Preferably the copolymer is an essentially linear copolymer of ethylene with propylene, such as a linear low density polyethylene (LLDPE).
Examples of CH2xe2x95x90CHR xcex1-olefin, wherein R is a C2-C8 alkyl radical, that can be present in heterophasic polymer composition (I) are 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene and 1-octene.
When present, the diene units in fraction (C) of (I) are preferably in an amount from 1% to 10% by weight with respect to the total weight of (C). Examples of dienes are butadiene, 1,4-hexadiene, 1,5-hexadiene and ethylene-1-norbornene.
The above-mentioned heterophasic olefin polymer composition (I) can be prepared by melt blending fractions (A), (B) and (C) in the fluid state, that is at temperatures higher than their softening or melting point, or by sequential polymerization in two or more stages in the presence of a highly stereospecific Ziegler-Natta catalyst. In particular the catalyst system comprises (i) a solid catalyst component containing a titanium compound and an electron-donor compound both supported on a magnesium halide and (ii) an Al-trialkyl compound and an electron-donor compound.
Examples of sequential polymerization processes are described in published European patent application EP-A-0 472 946. When heterophasic olefin polymer composition (I) is prepared by sequential polymerization, fraction (B) is present in an amount greater than or equal to 1% by weight. When said fraction (B) is present, it is preferable that the (B)/(C) weight ratio be less than 0.4, in particular from 0.1 to 0.3. It is also preferable that the weight percent of fraction (C), or of the sum of fractions (B) and (C), be from 50 to 90%, preferably from 65 to 80%, with respect to heterophasic olefin polymer composition (I).
Heterophasic olefin polymer composition (I) has preferably Melt Flow Rate (MFR) (according to ASTM D 1238, condition L) values generally comprised in the range from 0.1 to 100 g/10 min, preferably from 0.2 to 50 g/10 min. Heterophasic olefin polymer composition (I) having said values of MFR can be obtained directly during the polymerization process; otherwise heterophasic olefin polymer composition (I) can undergo a visbreaking process carried out in the presence of visbreaking agents, such as peroxides. The said visbreaking process is carried out according to well-known methods.
Preferably polymers 1 having the cited {overscore (M)}w/{overscore (M)}n ratio are obtained directly by the polymerization process, i.e. in the absence of chemical visbreaking, by peroxides for instance. Polymers 1 can be prepared with metallocene catalysts, for example.
Preferred examples of elastomeric polymers 1 are:
(a) elastomeric copolymers of ethylene with 1-octene having from 20 wt % to 40 wt % of 1-octene (13C-NMR analysis); preferably having density of less than 0.89 g/ml;
(b) elastomeric thermoplastic copolymers of ethylene with 1-butene having from 20 wt % to 40 wt % of 1-butene (13C-NMR analysis); preferably having density of less than 0.89 g/ml;
Preferred examples of elastomeric copolymers 2 are:
(c) ethylene-methyl acrylate copolymers containing about 20-25 wt % of methyl acrylate units and having MFR form 1.5 to 6 g/10 min.
Preferred examples of elastomeric copolymers 3 are:
(d) unsaturated linear block copolymers of styrene with isoprene or butadiene and saturated linear block copolymers of styrene with ethylene and butylene.
The copolymers of groups 1 to 3 are preferred. In particular copolymers (a) and (b) are more preferred, more particularly copolymers (a) are the most preferred.
A specific example of copolymers (a) is a copolymer containing 66 wt % of ethylene and 34 wt % of 1-octene (13C-NMR analysis, see note 2 below), having a hardness of 75 Shore A points, a MFR of 10 g/10 min and a density of 0.87 g/ml according to method ASTM D 792.
Another specific example of copolymers (a) is a copolymer containing 75 wt % of ethylene and 25 wt % of 1-octene (IR analysis), having a hardness of 75 Shore A points and a density of 0.87 g/ml according to method ASTM D 792 and MFR of about 1 g/10 min.
A specific example of copolymers (b) is a copolymer containing 77.9 wt % of ethylene and 22.1 wt % of 1-butene (13C-NMR analysis, see note 2 below) having a hardness of 85 Shore A points and a density of 0.87 g/ml according to method ASTM D 792.
A specific example of copolymers (c) is an ethylene-methyl acrylate copolymer containing 20 wt % of methyl acrylate, having a MFR of 1.5-2.5 g/10 min, a hardness of 89 Shore A points and a density of 0.945 g/ml according to method ASTM D 792.
Specific example of copolymers (d) are styrene-isoprene-styrene block copolymers (SIS), commercialised as Kraton D-1112, having a hardness of 34 Shore A points; styrene-ethylene-butylene-styrene block copolymers (SEBS), marketed as Kraton G-1652, having a hardness of 75 Shore A points; and styrene-ethylene-butylene-styrene block copolymers (SEBS), marketed as Kraton G-1657, having a hardness of 65 Shore A points. They all are commercialised by Shell.
A specific example of polymer 4 is the one having a molecular weight over 3,000,000; it is marketed by Nippon Zeon Co. LTD with the trademark Norsorex N.
The compositions of the present invention can also contain various additives generally used in the polymeric thermoplastic compositions, such as stabilizers, anti-oxidizing agents, anti-corrosion agents, anti-UV agents, carbon black, pigments, plasticizers and so on. Furthermore, the compositions according to the present invention can contain additives, flame retardants and fillers, such as mineral fillers, capable of giving particular properties to the articles for the manufacture of which the compositions are made.
The compositions of the present invention can be prepared by blending the components in an apparatus equipped with mixing elements, such as an internal mixer or extruder. For example one can use a Banbury mixer or single-screw Buss extruder or twin-screw Maris or Werner type extruder.
The composition of the present invention can be prepared in one or more stage(s). The order of mixing of the components is not relevant. The visbreaking of heterophasic olefin polymer composition (I) through visbreaking agents can be carried out in the presence of elastomeric polymer (II), and optionally other additives, as well as before adding elastomeric polymer (II) or after the addition thereof.
The compositions of the invention are generally obtained in form of pellets. These can be transformed into shaped manufactured articles by known injection, co-injection moulding, sequential injection moulding and blow moulding processes and transformed into laminates, which include films and laminates, by extrusion.
Generally speaking, preferably, the compositions of the present invention suitable for injection moulding processes have values of MFR ranging about from 2 to 100 g/10 min, preferably from 2 to 50 g/10 min. The compositions having lower values of MFR, such as from 0.1 to 2 g/10 min, preferably from 0.2 to 2 g/10 min, are suitable for extrusion processes.